RSX: use cache-line waits for event queue draining

Utilities/mutex.h

@@ -28,6 +28,11 @@ class shared_mutex final
 public:
 	constexpr shared_mutex() = default;
 
+	const atomic_t<u32>& raw() const
+	{
+		return m_value;
+	}
+
 	bool try_lock_shared()
 	{
 		const u32 value = m_value.load();

rpcs3/Emu/Cell/lv2/sys_rsx.cpp

@@ -245,8 +245,7 @@ void _sys_rsx_drain_event_queue(rsx::thread* rsxthr, u64 event_flags = umax, u64
 			break;
 		}
 
-		// Wait
-		thread_ctrl::wait_for(100);
+		utils::spin_on_cacheline_once(queue->mutex.raw(), 0u, 100);
 
 		// Check for timeout
 		if (wait_timeout_ms == umax)